Nitrobenzene

Nitrobenzene was first synthesized in 1834 and became widely used as a cheap artificial almond flavoring and shoe polish ingredient in the 19th century, causing documented poisoning deaths in industrial workers who absorbed it through their skin [1]. Today it is primarily an industrial intermediate: most nitrobenzene produced is reduced to aniline, which is then used in polyurethane isocyanate production (for foams in furniture and insulation) and in dye manufacturing [2]. Production facilities are concentrated in major chemical manufacturing regions, and environmental contamination occurs through industrial discharge and spills. Nitrobenzene has contaminated surface water and groundwater near chemical manufacturing facilities. Water from the Jilin City, China chemical plant explosion in 2005 released 100 tons of benzene and nitrobenzene into the Songhua River, a source of drinking water for millions [3].

Occupational inhalation and skin absorption in aniline and dye manufacturing facilities are the primary exposure routes [1]. Nitrobenzene is readily absorbed through skin at room temperature — workers who spill it or handle it without adequate protection develop rapid systemic toxicity. Community exposure occurs near production facilities through air emissions and from contaminated water [2]. Some nail polishes and shoe polishes historically contained nitrobenzene as a solvent or fragrance agent; these uses have largely been discontinued in developed countries [3].

Nitrobenzene's primary acute toxicity is methemoglobinemia — it oxidizes the iron in hemoglobin from its oxygen-carrying ferrous state to the ferric state that cannot carry oxygen [1]. This produces a characteristic blue-gray skin discoloration (cyanosis) even when blood oxygen levels are not critically low, because methemoglobin causes this color regardless of oxygen. Severe methemoglobinemia causes headache, dizziness, fatigue, shortness of breath, and in high exposures, loss of consciousness and death. Nitrobenzene is also a suspected human carcinogen [2]. The liver is affected by chronic exposures, and animal studies show thyroid, kidney, and bone marrow effects. Methemoglobin is treated with methylene blue given intravenously [3].

Workers in nitrobenzene production, aniline manufacturing, and dye synthesis face the highest occupational risks [1]. Individuals with inherited glucose-6-phosphate dehydrogenase (G6PD) deficiency are more sensitive to nitrobenzene's methemoglobin-forming effects because they have reduced capacity to reverse hemoglobin oxidation [2]. Communities near chemical production facilities with nitrobenzene releases face environmental exposure.

Workers in nitrobenzene environments: wear impermeable chemical gloves, protective clothing, and NIOSH-approved organic vapor respirators — skin absorption is a major route [1]. Regular methemoglobin monitoring (co-oximetry blood test) should be part of occupational health for workers with regular nitrobenzene exposure [2]. For community water contamination near chemical facilities, use certified carbon block or reverse osmosis filters [3].